Re: [PATCH] Add LED driven by multiple gpio.

[Jacek Anaszewski <j.anaszewski@samsung.com>]

Hi David,

On 04/26/2016 10:26 PM, David Rivshin (Allworx) wrote:
> On Mon, 25 Apr 2016 11:14:38 +0300
> Dmitry Bondar <bond@simicon.com> wrote:
>
>> Hello, on our board we have one LED with 2 gpio connected to it:
>>   - when gpio0 is on and gpio1 on - LED is orange.
>>   - when gpio0 is on and gpio1 off - LED is green.
>>   - when gpio0 is off and gpio1 on - LED is red.
>>   - when gpio0 is off and gpio1 off - LED is off.
>> We want use led_trigger (nand-disk) on this LED.
>> Below patch which we use for get one LED on 2 gpios.
>> Can be this in mainline, or may be exist other - better way?
>>
>
> It sounds like what you have is two independent GPIO controlled LEDs:
> one green and the other red (even if they are part of the same IC).
> Given the current infrastructure, I have modeled such cases as two
> separate LEDs in the devicetree, named <device>:green:<function> and
> <device>:red:<function>. Userspace is then responsible for controlling
> them appropriately to get the desired color.
>
> Unless I'm mistaken, in your case (nand-disk) there are blinking
> combinations you wouldn't be able to achieve this way, but there
> are a number you can do:
> - off/green:  	green:nand-disk	red:off
> - off/red: 	green:off 	red:nand-disk
> - off/orange:	green:nand-disk	red:nand-disk
> - green/orange:	green:on	red:nand-disk
> - red/orange:	green:nand-disk	red:on
> The other cases (e.g. green/red) would need an inverted nand-disk
> trigger (on while inactive, off while active).
>
> I'm hoping that if the RGB LED framework comes to fruition, that there
> will be some way to combine arbitrary single-color LED devices into a
> logical RGB LED.

It turns out that rgb-pattern trigger, we were discussing some time ago,
would be useful also for LEDs of arbitrary colors. It should be given
more generic name then, e.g. three-led-composite or so. The "color"
sysfs attribute exposed by the trigger could be replaced with
"subled_id", that would accept values 0, 1 or 2.

Brightness of such a compound LED could be set with:

led_trigger_3led_event(sturct led_trigger *trig,
                        enum led_brightness led1,
                        enum led_brightness led2,
                        enum led_brightness led3)

Maybe we should think about making this scalable using
C ellipsis feature:

led_trigger_3led_event(sturct led_trigger *trig,
                        enum led_brightness led1,
                        ...)

-- 
Best regards,
Jacek Anaszewski